Interested in getting one of these, been reading a ton about them and all of the parts available for them.

I have a few questions:

Are they just as capable as a full-size rig, or one of those four-letter genres?
How fast do they go (when decked out and modded to support, say, 32-33" tires)?
Do they have sufficient torque available to go up any terrain?
After building yours up, and considering all of the time and money put in: If you were to do it all over again, would you still do it? Would you do something bigger?